If your furnace isn’t turning on, a blown fuse could be to blame. Most new furnaces have a fuse. Like with other fuses, it’s a safety device that protects against overcurrent. Fuses can blow, however. And until you replace the blown fuse, you won’t be able to use your furnace.

The Purpose of a Furnace Fuse

Most new furnaces have a fuse to protect against overcurrent. Overcurrent can cause serious damage to furnaces. If there’s too much current flowing to a furnace – current is measured in amperage – the furnace’s electrical parts may fail.

Electric furnaces use electricity to generate heat, but even gas furnaces use electricity to power the blower. To protect against overcurrent, most of them have a fuse. It’s usually found in the control board near the blower.

How Furnace Fuses Work

Furnace fuses work by allowing a limited amount of current to pass through them. Some furnace fuses are rated for 3 amps, whereas others are rated for 5 amps. Regardless, they will only allow the current for which they are rated to pass through.

If the current is greater than that for which a furnace fuse is rated, the fuse will blow. Blown fuses are characterized by a broken conductive pathway. New, functional fuses have a complete conductive pathway. This means electricity can travel through a new fuse. Excess current, though, will cause fuses to blow.

Furnace fuses and other types of fuses are designed to blow when exposed to excess current. Excess current will typically break the conductive pathway within the furnace fuse. With a broken conductive pathway, electricity won’t be able to reach the furnace.

Fixing a Blown Furnace Fuse

If your furnace has a blown fuse, you’ll need to replace it. Most furnaces won’t turn on with a blown fuse. You may still be able to run the air conditioning system, but the furnace won’t run with a blown fuse.

Fortunately, furnace fuses are inexpensive. You just need to purchase a furnace fuse with the same amperage rating and size as the existing, blown furnace fuse. After pulling the blown fuse from the control board, you can insert the new fuse.

You can contact a professional heating, ventilation and cooling (HVAC) technician for assistance as well. Maybe you can’t find the fuse, or perhaps you aren’t sure which type of fuse you need to replace it with. A professional HVAC technician can replace your furnace’s blown fuse while restoring heat to your home.